A data programmable disk medium to which users are capable of recording a program such as audio data is well known and a disk system which has introduced a magneto-optic disk, for example, as a recording medium is already popular.
In this disk system, an audio signal is sampled at 44.1 kHz and quantized at 16 bits for conversion into digital audio data. Thereafter, this digital data is then subjected to audio compression process for creation of data recorded under the condition that it is compressed to one-fifth.
Therefore, in the data recovery apparatus, decoding is then required to expand, on the contrary, the data read from a disk. That is, after the data is recovered to the initial condition through the decoding operation, the data is then converted into analog audio signal.
While the disk system is utilized widely for variety of applications, it may be used for recording and recovery not only of audio signal but also of interview or conference data.
Along with variety of applications explained above, as a data recording and recovery apparatus, a small size and portable apparatus is just suitable and an apparatus also assuring monaural recording as well as stereophonic recording has been developed in response to the requirement for long-term recording. In the monaural recording, since the amount of data per unit time is reduced to a half, the recording time can be extended up to twice in comparison with that of the stereophonic recording.
When a battery-driven portable type data recording and recovery apparatus, for example, is discussed, it is a critical problem that the operation life of battery such as dry battery or chargeable battery used can be extended by saving the power consumption.
However, sufficient development has not yet been achieved for saving of power consumption in the data decoding for the audio compression system described above.
In consideration for such background, it is an object of the present invention to provide a decoder and a power saving data recovery apparatus.